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Geolagccal Tec"Cs 1AC Page 5 GW Monitonng Report Ted Peters-AST Project No 701 2 May 15, 2003 30 FINDINGS AND DISCUSSION ' The results of the groundwater sample analyses show the following • Groundwater samples from three of the five AST monitoring wells (MW-4, MW-6 and MW-7) reveal the presence of TPH-G or gasoline constituents Well MW-5 probably contains TPH-G but the detection limits are elevated due to the presence of high levels of TPH-D • Well MW-5 contained TPH-D at 212,000 µg/l, which is the highest recorded amount ' thus far in the investigation • A heavy sheen of product was noted in MW-5 for this event This well has contained free product during previous events • Well MW-8 contained trace BTEX constituents at concentrations dust above the laboratory reporting limits for the January 2003 event This was the first time since the well's installation in March 2001 that it has contained detectable contamination It has now returned to non-detectable levels 0 Oxidation-Reduction Potential (ORP) and Dissolved Oxygen (DO) measurements (Table 3) suggest that all of the AST wells are in the core of the contamination plume or ' are immediately down gradient of the plume Negative ORP values and low DO values indicate that the wells are within the halo of reaction depleted water caused by biodegradation of the contaminants For the April 2, 2003 event, three wells MW-5, MW-6 and MW-7 had negative ORP values MW-4 is in the vicinity of the primary contamination sources (diesel ASTs) and MW-8 is perpendicular to gradient • Figure 4 illustrates TPH-G concentrations in groundwater in the vicinity of the former ' ASTs The highest level of TPH-G detected is in well MW-4, which is different from past events, which showed that MW-7 on the northwest side of the parcel had the highest concentrations Well MW-5 has previously contained the highest levels of TPH- G but contained free product sheen for this event ' • Figure 5 illustrates TPH-D concentrations in groundwater in the vicinity of the former ASTs Well MW-5 contained free product sheen GTI's previous GeoProbe investigation revealed that the diesel contamination is limited to the area of former ASTs ' and associated dispensers 4 0 CONCLUSIONS & RECOMMENDATIONS Conclusions I Groundwater flow is predominantly to the northwest for both the AST and UST sites on this property GTI believes that previous southwesterly directions noted in the AST area are anomalous based on the presence of free product in MW-5 and/or the spatial orientation of the wells ' 2 TPH-G, TPH-D or volatile organic compounds are present in four of five groundwater monitoring wells 3 The TPH-G concentrations exhibit a decreasing trend in the downgradient well MW-7 ' Figure 6 Well MW-7 TPH-G & Benzene versus Elevation illustrates this situation 4 The methylene chloride found in MW-4 through MW-7 is believed to be a lab l contaminant and not present in groundwater aquifer